Field of the Invention
The present invention relates to a method for preparing size-controlled gold nanoparticles and a colorimetric detection method of strong acid using them, and more particularly, to a method for preparing hydrophobic gold nanoparticles, capable of controlling sizes of particles over a broad range by preparing gold nanoparticles with regulating volume ratio of two types of surfactant, and a colorimetric detection method of strong acid, capable of detecting up to low content hydrochloric acid of 5 ppm by utilizing the phase transited hydrophilic nanoparticles in colorimetric detection for detecting aqueous strong acid after phase-transiting the prepared hydrophobic gold nanoparticles into hydrophilic gold nanoparticles.
Description of the Related Art
Metal nanoparticles, among nano-size materials, have chemical and physical properties distinguishable from bulk metals, so the metal nanoparticles have been widely used in various fields. This is because surface area of a metal increases greatly when the metal reduces to nano size from a bulk state, and only small numbers of atoms exist in a nanoparticle and thus it exhibits unique catalytic, electric, photo-electric and magnetic properties. Such nanoparticles become superior catalysts having high surface-to-volume ratio due to their small size. Additionally, nanoparticles have relatively large surface tension and the surface tension activates remarkably atoms on the surface of the nanoparticles. Metal nanoparticles have been widely used in various fields such as energy conversion, photo catalyst, green chemicals, non-symmetric synthesis, biomimetic technology, molecular printing technology.
Gold nanoparticles are elements having also nano-size molecular structures and their surface-to-volume ratios vary depending on their sizes and thus the gold nanoparticles exhibit various electrical, optical and biological properties according to their spatial structures and orders of one, two and three dimension. Accordingly, researches for controlling the sizes of gold nanoparticles are being made progressively in various applications, and until now, researches to adjust the size of gold nanoparticles by controlling reaction temperature, reaction time, and concentration of reactants have been made.
Meanwhile, hydrochloric acid is used for removing rusts in iron oxide, etc., or plating metals in the industrial sites. Additionally, hydrochloric acid is also used in large scale processes of manufacturing organic compounds such as vinyl chloride, PVC, poly urethane, etc., and in manufacturing process of food additives such as gelatin and leather treatments and so on. With the rapid progress of industrialization and its large scale growth, the amount of hydrochloric acid used in the industry is increasing. When hydrochloric acid is exposed to natural environment and human, dehydration through the combination with protein of an organic matter is caused to occur, exhibiting harmful effects such as destruction of protein structure, damage to cell membrane, and destruction of cell, etc. In order to prevent such harmful effects, researches for detecting the amount of hydrochloric acid in the water are being made actively. Conventionally, the methods for detecting hydrochloric acid are performed by observing the variations of electrochemical property, optochemical property, mass, and imaging, etc., thereof. Most of those methods are performed to detect hydrochloric acid in a gaseous phase, however, various kinds of salts and acids exist in the water and thus it is difficult to detect specially only minute amount of hydrochloric acid.
Recently, a method has been developed for calorimetric detection of 100 ppm of hydrochloric acid by using a phenomenon where gold nanoparticles are corroded with hydrochloric acid to reduce their sizes and change color of the solution thereof. However, the level of 100 ppm is higher than the allowance standard of concentration about hydrochloric acid exposure prescribed by United States Department of Labor. Accordingly, it is necessary to develop a method for detecting simply and rapidly hydrochloric acid of ultralow concentration.